<?php  
	session_start();
	getCode(4,50,25);
	
function getCode($num,$width,$height) { 
	$pattern="0123456789abcdefghijklmnopqrstuvwxyz";
    $code = ""; 
    for ($i = 0; $i < $num; $i++) { 
        $code .= $pattern{rand(0, 35)}; 
    } 
    //保存验证码到session
    $_SESSION["confirm_code"] = $code; 
    //创建图片，定义颜色值 
    header("Content-type: image/PNG"); 
    $im = imagecreate($width, $height); 
    $black = imagecolorallocate($im, 0, 0, 0); 
    $gray = imagecolorallocate($im, 200, 200, 200); 
    $bgcolor = imagecolorallocate($im, 255, 255, 255); 
    //填充背景 
    imagefill($im, 0, 0, $gray); 
 
    //画边框 
    imagerectangle($im, 0, 0, $width-1, $height-1, $black); 
 
    //随机绘制两条虚线，起干扰作用 
    $style = array ($black,$black,$black,$black,$black, 
        $gray,$gray,$gray,$gray,$gray 
    ); 
    imagesetstyle($im, $style); 
    $y1 = rand(0, $height); 
    $y2 = rand(0, $height); 
    $y3 = rand(0, $height); 
    $y4 = rand(0, $height); 
    imageline($im, 0, $y1, $width, $y3, IMG_COLOR_STYLED); 
    imageline($im, 0, $y2, $width, $y4, IMG_COLOR_STYLED); 
 
    //在画布上随机生成大量黑点，起干扰作用; 
    for ($i = 0; $i < 50; $i++) { 
        imagesetpixel($im, rand(0, $width), rand(0, $height), $black); 
    } 
    //将数字随机显示在画布上,字符的水平间距和位置都按一定波动范围随机生成 
    $strx = rand(3, 8); 
    for ($i = 0; $i < $num; $i++) { 
        $strpos = rand(1, 6); 
        imagestring($im, 5, $strx, $strpos, substr($code, $i, 1), $black); 
        $strx += rand(8, 12); 
    } 
    imagepng($im);//输出图片 
    imagedestroy($im);//释放图片所占内存 
} 
?>